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Exploring Heat and Density:

The Big Ideas about Density

Focus Question: What is density?

Casually speaking, the amount of “stuff” in a given space.

More specifically, density = mass/volume – a measure of how much mass there is per volume.

Focus Question: How does temperature affect density?

  • When a liquid or gas is heated, the molecules move faster, bump into each other, and spread apart. Because the molecules are spread apart, they take up more space. They are less dense.

  • The opposite occurs when a liquid or gas is cooled. The molecules move more slowly and take up less space.

  • Therefore temperature can affect density.

Focus Question: How can we use density to explain why some things float and others sink?

  • Each substance has its own density, based upon the amount of mass per volume.

  • Water has a density of one.

  • Liquids and solids with a density greater than one will sink.

  • Liquids and solids with a density less than one will float

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